332 The Philippine Journal of Science 1920 
Table 7. — Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of copper sulphate. 
[Date of test, February 3, 1920 ; date of observation, February 6, 1920.] 
r 
Exposure. 
Dilution. 
1 to 50,000. 
1 to 20,000. 
1 to 10,000. ' 
1 to 6,000. 
.... 1 
1 to 2,000. | 
o 
o 
© 
o 
+-> 
T— 1 
1 to 500. 
1 to 200. 
© 
o 
o 
4-> 
1 to 50. 
Min. 
sec. 
2 
30 
+ 
+ 
+ 
+ 
+ 
»+ 
»+ 
— 
— 
— 
5 
00 
+ 
+ 
+ 
+ 
— 
— 
— 
— 
— 
— 
7 
30 
+ 
+ 
+ 
b 
10 
00 
+ 
+ 
+ 
b— 
12 
30 
+ 
+ 
+ 
L 15 
00 
+ 
+ 
+ 
a Tube tested for P. citri, February 5, 1920 ; positive, February 7, 1920. 
*> Tube tested for P. citri, February 5, 1920 ; negative, February 7, 1920. 
The results with copper sulphate at more finely graduated di- 
lutions could not be made to agree. In the five tests employed 
a dilution of 1 to 200 gave negative results at all lengths of ex- 
posure. A dilution of 1 to 500 was toxic to the canker bacteria 
at 2% minutes exposure in only one test. Exposures of 5, 7% , 
10, 12%, and 15 minutes at the same dilution were negative in 
all tests. The dilutions of 1 to 1,000 and 1 to 2,000 were posi- 
tive in all tests at 2% minutes, but varied for exposures of 5, 
7%, 10, 12%, and 15 minutes. One to 5,000 was positive at all 
exposures in all tests. In view of the considerable variation 
in results for the five tests it is not safe to consider any dilution 
of copper sulphate above 1 to 200 or 1 to 300 as a disinfectant 
for Pseudomonas citri. This is of interest in view of the prob- 
able weak dilutions of copper salts which are made available 
by the weathering of Bordeaux mixture and other copper sprays 
upon trees, and seems to indicate that the toxic action of such 
copper sprays would have little value in preventing citrus-canker 
infection if dependent only on the soluble copper salts liberated 
upon the foliage. 
Repetition of the tests with dilutions of Bordeaux 4-4-50 mix- 
ture was made eight times ; the results show considerable varia- 
tion in the bactericidal value of Bordeaux 4-4-50 mixtures. 
Tests were made which showed a killing action at as low a 
dilution as 5 per cent for a length of exposure of 5 minutes. 
More commonly, however, killing has only been obtained with 
